In a recent vehicle braking control system, ABS control has been widely adopted. In general, when a vehicle body is decelerated upon suddenly braking a vehicle, a braking force increases before a sufficient load is transferred to a vehicle wheel, so that the vehicle wheel tends to be locked. Then, the ABS control is started, and the control device decreases a fluid pressure P of a wheel cylinder. At this time, the timing of starting the ABS control is defined by a relation between a slip ratio S and a predetermined setting value. Further, the setting value is set based on a road surface friction coefficient μ according to a predetermined characteristic μ-S.
However, when the road surface friction coefficient μ of the traveling road is higher than the setting value (for example, a dry road surface or the like), the compression gradient of the fluid pressure P is not sufficient, and hence the braking force is not sufficient, so that the braking distance increases in length. On the contrary, when the road surface friction coefficient μ of the traveling road is lower than the setting value (for example, a wet road surface or the like), the ABS control is actuated at an early timing, and also the braking force is not sufficient, so that the braking distance increases in length. Accordingly, there is a problem in that the robustness of the braking control may not be ensured with respect to a change in the road surface friction coefficient μ of the traveling road.
Furthermore, as the existing vehicle braking control system having such a problem, a technique disclosed in Patent Literature 1 is known.